The first record of a nearly complete choristodere (Reptilia: Diapsida) from the Upper Jurassic of Hebei Province, People’s Republic of China

Abstract

Choristodera are freshwater aquatic reptiles known from the Middle Jurassic to the Miocene. Their fossil record shows a peak in diversity in the Early Cretaceous of eastern Asia, most notably in the Jehol Biota of China but also in Japan and Mongolia. However, until now, the only Jurassic records from Asia have been rare disarticulated elements from Middle Jurassic microvertebrate sites in Transbaikalian Siberia, with a possible jaw fragment from the Late Jurassic of Xinjiang, China. Here we describe Coeruleodraco jurassicus gen. et sp. nov., a new, fully articulated choristodere skeleton from the Tiaojishan Formation of China, which is considered to be of Late Jurassic (Oxfordian) age. As such, the new specimen represents the first complete Jurassic choristodere recovered worldwide, and also provides important information on the pre-Cretaceous history of the group in eastern Asia. In its proportions and postcranial characters the new taxon resembles previously described Asian taxa such as Philydrosaurus, but it is distinct in possessing several apparently plesiomorphic characters, including a short antorbital region, paired external nares and an open lower temporal fenestra. Phylogenetic analysis places the new choristodere as the sister taxon of a non-neochoristoderan clade comprising Asian and European taxa, whereas the European Jurassic Cteniogenys becomes the sister taxon to all other Choristodera. http://zoobank.org/urn:lsid:zoobank.org:pub:5478E013-CC19-487A-ACC0-021A88633338